Bacterial DNA and its synthetic oligonucleotide (ISS-ODN, also known as CpG motives) inhibit allergic inflammation. Paradoxically, ISS-ODN, like other microbial TLR ligands, activate the innate immune system to release pro-inflammatory mediators. Therefore, this project will explore the profound anti-inflammatory effects induced by ISS-ODN in animal models of experimental allergy. Based on our data we hypothesize an essential and orchestrating role for ISS-induced activation of interferon regulatory factor (IRF)-1 pathway in mediating the anti-inflammatory effects of ISS-ODN. This project has been designed to identify the subsequent biochemical and molecular pathways that synergize to inhibit allergic inflammation at the level of innate immunity. We will explore the role of IRF-1 pathway in TLR ligand-mediated signaling and investigate the impact and relative contribution of several ISS-induced, IRF-1 target genes (or their metabolites) to the inhibition of allergic inflammation (SA-1). These target genes include type 1 (IFN (SA-1), indoleamine 2, 3-dioxygenase (SA-2) and certain COX2 metabolites (SA-3). Complementary studies addressing the role of genetic and environmental factors as well as the impact of adaptive immunity on the inhibition of allergic inflammation by microbial TLR ligands will be performed by the other projects of this program. We anticipate that the results from these studies will provide a molecular basis for the hygiene hypothesis by demonstrating a physiological role of TLR-mediated signaling/cell activation in the prevention of the allergic phenotype. Furthermore, it will provide a better molecular and biochemical understanding mandatory for the design and success of future clinical trials with ISS-ODN and/or microbial TLR ligands in allergic disease.